Lab 1 Diffusion and Osmosis

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AP Biology November 3, 2011 Lab 1: Diffusion and Osmosis Objectives: * Measure the water potential of a substance in a controlled experiment. * Determine the osmotic concentration of living tissue or an unknown solution from experimental data * Describe the effects of water gain or loss in animal and plant cells * Release osmotic potential to solute concentration and water potential Introduction: Diffusion is the process that allows particles or molecules to move from an area of high concentration to an area of low concentration. This process accounts for the movement of many small molecules across cell membranes. The rate of diffusion of particles will be affected by the steepness of the concentration gradient or the difference in concentration between two areas. Diffusion can only occur across a membrane if there is a concentration gradient and the membrane is passable. If neither one is present, diffusion won’t occur. The size of the tiny pores in a membrane, among other things, decides which particles can diffuse across the membrane. The process of a solute moving through a semipermeable membrane is known as dialysis. Osmosis is a specialized case of diffusion that involves the passive transport of water. In osmosis, water moves through a semipermeable membrane from a region of higher concentration of water to a region of lower concentration. When two solutions have the same concentrations of a solute they are said to be isotonic. When one solution has more solute than another solution it is said to be hypertonic to the other. When one solution has less solute than another solution it is said to be hypotonic. In osmosis, the concentration of water is more important than the concentration of solute. If two solutions of unequal concentrations of a solute are separated by a semipermeable membrane the water can pass through but the solute

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